Sep-2020

Tru-Grid™ scans detect solids build-up to assist in determining the appropriate maintenance path

PackView™ liquid retention scale included on Tru-Grid™ Scan results provide customers the amount of build-up, relative density and growth patterns saving customers thousands of dollars.

Article Summary

Solids material can accumulate or develop in chemical and refinery units under various conditions. In most cases, in piping, vessels or exchangers it can be a challenge to remove it while the unit is online. It also creates flow limitations and degrading unit performance. If this build remains unchecked, it can produce blockages that can shut portions of an operating unit down or even an entire complex. Tracerco customers would like to understand the amount of build-up along with its relative density and growth pattern.

The Field Test

Tracerco was asked to scan a customer’s mist eliminator in the upper portion of an operating vessel. The tower had been in operation for 20+ years and never been opened to inspect the mist eliminator. There was also an identical vessel with the same mist eliminator, which was also scanned during the same project. Tracerco performed a Tru-Grid™ Scan to identify the placement of the mist eliminator along with the density responses in each quadrant. A PackView™ density scale is overlaid on Tru-Grid™ Scan results to determine the mist eliminators liquid retention or possible solids accumulation.

The mist eliminator consisted of a tightly woven wire mesh blanket, 6 inches (15 cm) in depth. This design prevents liquid mist droplets from progressing through to an adjacent piece of equipment or vessel. It has the general structure and density signature of wire gauze packing, which is used throughout petrochemical industries.

A Tru-Grid™ Scan consists of four individual vertical scans of the vessel, oriented in a four-quadrant grid pattern. Tracerco’s proprietary PackView™ liquid retention scale is a calculated density scale based on the radiation attenuation through the eliminator and is provided on Tru-Grid™ Scan results to measure densities within the mist eliminator. PackView™ enables our client to observe density variations within the bed to identify liquid retention, packing material and any other substances in the packing.

The Analysis
The manufacturers drawings specified the mist eliminators dry density was 154 lb/ft3 (2467 kg/m3). However, the PackView™ liquid retention scale showed the mist eliminator to be holding between 60.0-75.0 lb/ft3 (961 - 1201 kg/m3) of solids material (Figure 1). There also appeared to be approximately 2 inches (5 cm) of additional solids, which had accumulated in the top southeast quadrant of the mesh indicated by the red and green scanlines.

Figure 3 is an overlay of the two vessels grid scan results showing the different densities found in each of the mist eliminator scans.

Tracerco was also requested to perform a Tru-Grid™ Scan on the identical adjacent vessel (Figure 2). Ironically, this vessel showed no indication of solids accumulations within the mist eliminator and was operating between 1.0-2.0 lb/ ft3 (16 - 32 kg/m3) above its 15.0 lb/ft3 (240 kg/m3) dry density.
 
The Conclusion
The unit was shutdown a few months later and the client confirmed the Tru-Grid™ Scan findings of the solids build-up in the mist eliminator. They also elected not to open up the second vessel which had no signs of build-up, saving them an additional two days off their shutdown resulting in two days of gained production time and saved downtime costs. Using PackView™ to understand the extent of solids buildup proved to be an effective method in determining the appropriate maintenance path of the vessels.